Photographic fixing bath



Patented June "8, 1943 UNITED STATES PATENT rnorooinirnrc FIXING BATH James R. Alburger, Merion, Pa., assignor to Radio.

Corporation of America, a corporation of Dela-r ware I Serial No. 306,971

No Drawing. Application November 30, 1939,

4 Claims.

This invention relates to an improved photographic fixing bath, and more particularly to a fixing bath which is adapted for. use at abnormally high temperatures and which can be used after the use of a highly alkaline developer without causing reticulation.

The usual types of fixing baths are either practically neutral or are somewhat acid and include, in addition to the sodium thiosulphate,

which dissolves the undeveloped silver salts, an

. developed film is placed in a fixing bath having an alkalinity approaching that of'the developer no such reticulation occurs and a correspondingly improved photographic image results.

If an appropriate alkali is added to a sodium thiosulphate solution of ordinary concentration, it tends to soften the emulsion and render the film liable to damage in handling, and reticulation is likely to occur when the film is placed in the succeeding wash. The addition of an ordinary hardening agent to such a fixing bath does not prevent this difficulty, since thesoftening of the gelatine occurs before the hardening agent has time to become effective.

I secure the necessary degree of alkalinity without the foregoing objections and with a hardening, instead of a softening of the gelatine 'by balancing the alkali with alum. The alum reacts with the alkali to first form aluminum hydroxide, which tends to be precipitated and to then the emulsion when either th developer or fixing bath are used at high temperatures. v

Another object of the invention is to provide a fixing bath which will automatically recover the dissolved silver.

Other and incidental objects of the invention will be apparent .to those skilled in the art from a reading of the following specification.

In the preparation of my imp fix bath I use the usual sodium thiosulphate as a fixer,

and I may also add paraformaldehy e as an additional hardener. The balancing of the alkali and alum may be accomplished as described and claimed in my applications Serial No.

205,362 and 205,363, both filed April so, 1938, now U. S. Patents Nos. 2,199,903 and 2,199,904,

respectively, of May 7, 1940, whichgdescribe such a balanced solution of alkali and alum applied to a developer.

A typical formula for my improved fixing bath is as follows:

The proportion of alum and sodium hydroxide .'is, as indicated above, in the general ratio of 4:3.v The quantity of sodium hydroxide used, however, is determined by the alkalinity of the developer which preceded the fixing bath. If

the developer is highly alkaline, the fixing bath.

' should have substantially the same alkalinity which can be determined as usual by the pH value. Since there is no change in the alkalinity of the solution in which the film is immersed,

form an aluminate which remains in s0llltion,.

but which has a hardening action on the gelatine. If the alkali is used up by oxidation, or otherwise, a corresponding amount of aluminum hydroxide is precipitated, thereby maintaining the alkalinity of the bath constant.

One object of the invention is. to provide an improved fixing bath.

Another object of the invention is to provide a fixing bath which may be' used at relatively high temperatures.

Another object of the invention is to provide a fixing bath which will prevent reticulation of there is then no tendency toward reticulation inpassing the film from one solution to the other, while the hardening action of the fixing 'bath is suificient to prevent any tendency toward reticulation when the film i immersed in the subsequent wash water." I

As pointedout above, there is. a tendency for the alkali in the fixing bath to be gradually oxidized by the air in contact with the surface thereof, and particularly when motion picture film, by the used for developing air carried into the bath by-the film, and this oxidation releases a corresponding amount of aluminum hydroxide from solution. This aluminum hydroxide settles out in the form of a gelatinous precipitate. Since the fixing bath OFFICE is' alkaline and not acid, it does not suddenly stop the action of new' developer in the emulsion, as would an acid fixing bath.

The consequence of this is that any developer ,in the emulsion goes into solution in the fixing bath and reduces the dissolved silver in the fixing bath. 'This reduced silver, which is practically in colloidal form, is precipitated with the aluminum hydroxide and the silver may b readily recovered from the resulting sludge. A further result of this action is that the fixing bath does not become saturated with silver salts and maintains its original activity over a'relatively long time. I! an insuflicient quantity of developer to accomplish. the regeneration of the fixing bath is carried over by the film, small additional quantitles of developer may be added to the fixing bath for this purpose, and partly spent developer 'may be used, thereby recovering not only the silver in solution in the fixing bath, but also that in solution in the developer.

to the degree to which the polymerization has occurred.

I claim as my invention:

1. A photographic fixing bath containing a.

solvent of silver salts, an alum, and suillcient alkali to dissolve the aluminum compound tending to be precipitated by the alkali.

2. A photographic fixing bath containing a solvent of silver salts, an alum, suflicient alkali to n will be apparent to those skilled in the art that the proportion of sodium thiosulphate or hypo" in the solution may be varied according to'the requirements 0! the'work at hand, and it will be also apparent that not only should the alkalinity be varied aspointed out, but that the quantity of para-formaldehyde should be varied according to the degree or hardening desired. Ordinary formaldehyde may, of course, 'be added dissolve the aluminum compound tending to be precipitated by the alkali, and a hardening agent.

3. A photographic fixing bath containing sodium thiosulphate, analum, and sufllcient alkali to dissolve the aluminum compound tending to be precipitated by the alkali.

4. A photographic fixing bath containing sodium thiosulphate, a solvent of silver salts, an alum, suflicient alkali to dissolve the aluminum compound tending to be precipitated by the al-- kali and a hardening agent.

JAMES 'R. ALBURGER. 

